This invention relates to a wireless communications system providing call transfer for an incoming call to a mobile subscriber unit.
Wireless communications systems attempt to provide telephone services to mobile subscribers that are equivalent to traditional landline telephone networks. This objective is complicated by the fact that mobile subscribers may roam away from their home market. Different wireless markets may utilize different manufacturer""s equipment. Consequently, mobile subscribers may not be able to use wireless features offered in their home markets if the serving markets do not support the features.
As an example, xe2x80x9ccall transferxe2x80x9d is a common landline telephone service in which a subscriber can transfer an incoming call to another designated telephone party. However, this service is not always available in a wireless communications system. Not all mobile switching centers (MSC), which provides the switching functionality of a wireless communications system, support call transfer. If an incoming call is delivered to the mobile subscriber""s home market that supports call transfer and the mobile subscriber has roamed to another (serving) market, call transfer may not be available to the mobile subscriber. Moreover, even if call transfer is supported by the plurality of MSC""s which an incoming call spans, the prior art requires that inter-MSC telephone facilities be configured between the MSC""s. Having to support these facilities increases the cost to the wireless service provider, thus increasing the price of service to the wireless subscriber. Thus, there is an important need to provide ubiquitous call transfer to the wireless subscriber.
FIG. 1 illustrates an architecture supported by a wireless communications system that supports an incoming call to a mobile subscriber unit associated with a wireless subscriber in accordance with prior art. In FIG. 1, an incoming call originates from public switching telephone network (PSTN) 100 for mobile subscriber unit 105. The incoming call is delivered to originating mobile switching center (xe2x80x9coriginatingxe2x80x9d MSC) 101 (in which mobile subscriber unit 105 may or may not be located) through telephone facility 106. Typically, mobile subscriber unit 105 is provisioned (homed) at originating MSC 101, and PSTN 100 delivers all incoming calls to originating MSC 101.
If mobile subscriber unit 105 is not located within a region served by originating MSC 101, the incoming call must be delivered to serving mobile switching center (serving MSC) 103 in which mobile subscriber unit 105 is located. Originating MSC 101 determines where mobile subscriber unit is located by querying home location register (HLR) 102 using data facility 107. Whenever mobile subscriber unit 105 changes locations so that it is located in a region of a different serving MSC, HLR 102 is updated with the updated location through data facility 109. HLR 102 may be physically separate entity or may be physically located at originated MSC 101. The incoming call is delivered to serving MSC 103 through inter-mobile switching center (inter-MSC) facility 108. Serving MSC 103 connects the incoming call through base station 104 (where mobile subscriber unit is currently located) over trunk 110. Base station 104 establishes radio connection 111 to mobile subscriber unit 105, thus completing the incoming call between PSTN 100 and mobile subscriber unit 105. The telephone path of the incoming call consists of telephone facility 106, inter-MSC facility 108, trunk 110, and radio connection 111. Since the telephone path is completed at serving MSC 103, if serving MSC 103 is situated in a billing zone that is associated with long-distance rates, the party initiating the incoming call may be charged at a long-distance rate even though the designated party to which the call was transferred is not in a billing zone that is charged at a long distance rate.
FIG. 2 presents a message flow for transferring an incoming call (from PSTN 100) by mobile subscriber 105 to a designated party served by PSTN 100 in accordance with prior art. PSTN 100 uses telephone facility 206 to deliver the incoming call to originating MSC 101. Originating MSC 101 queries HLR 102 by sending LOCREQ message 207 in order to determine the current location of mobile subscriber 105 to route the call to the appropriate serving MSC 103. (Message 207 is specified in American National Standards Institute ANSI-41.) Message 207 includes a BILLID parameter equal to O-CALLID to identify the call identification as assigned by originating MSC 101. Consequently, HLR 102 sends ROUTREQ message 208 (specified in ANSI-41) to serving MSC 103 to determine the preferred method of routing the incoming call to serving MSC 103. Message 208 contains the BILLID parameter equal to O-CALLID. Serving MSC 103 returns this information using routreq message 209 (specified in ANSI-41). Message 209 contains the BILLID parameter equal to S-CALLID, which is the call identification assigned by serving MSC 103. Consequently, HLR 102 is able to relate the call identification assigned by originating MSC 101 (O-CALLID) with the call identification assigned by serving MSC 103 (S-CALLID) of the incoming call. Serving MSC 103 establishes a trunk to base station 104, in which the mobile is located, in preparation for supporting the incoming call. Base station 104 consequently establishes radio connection 212 to mobile subscriber unit 105.
HLR 102 returns the location of mobile subscriber unit 105 to originating MSC 101 by sending locreq message 211 (specified in ANSI-41). Message 211 contains the BILLID parameter equal to S-CALLID. Originating MSC 101 then establishes a connection to serving MSC 103 through inter-MSC facility 213. Inter-MSC facility 213 corresponds to inter-MSC facility 108 in FIG. 1. At this point of time, the incoming call to mobile subscriber unit 105 has been completed.
If mobile subscriber unit 105 wishes to transfer the incoming call to a designated party (and consequently causing mobile subscriber unit 105 to be disconnected from the call), mobile subscriber unit sends call transfer request message 214 to base station 104. Message 214 is dependent upon the air interface technology, e.g. Advanced Mobile Phone Service (AMPS), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), and Groupe Special Mobile (GSM), being supported by base station 104. (The specific messages for each air interface technology are known to one skilled in the art.) Base station 104 relays this request to serving MSC 103 utilizing facility request message 215. Messages 214 and 215 contain dialed digits generated by mobile subscriber unit 105. The dialed digits are interpreted by serving MSC 103 to signify a request for call transfer to a designated party. Serving MSC 103 establishes outgoing facility 216 and connects the incoming call to the designated party. At this point of time, the telephone path consists of telephone facility 206, inter-MSC facility 213, and outgoing facility 216.
Serving MSC 103 initiates the removal of radio connection 212 by sending disconnect message 217, which in turn causes base station 104 to send disconnect message 218 to mobile subscriber unit 105. Disconnect message 218 is dependent upon the air interface technology.
In the prior art, the mobile subscriber unit can be afforded call transfer service only if the serving MSC supports call transfer. In other words, even if the originating MSC supports call transfer, the mobile subscriber unit cannot initiate call transfer if the serving MSC does not support it. The present invention does not require the serving MSC to support call transfer in order for the mobile subscriber unit to obtain a call transfer of an incoming call. Moreover, the number of required telephone facilities is reduced.
The apparatus and method of the present invention enables a wireless communications system to transfer an incoming call by utilizing call processing at a serving mobile switching center, an originating mobile switching center, and a home location register.
The serving mobile switching center (where the mobile subscriber unit is located) executes program instructions to generate a query to the home location register in response to a request for a call transfer from the mobile subscriber unit. The home location register executes program instructions that interpret the query from the serving mobile switching center and instructs the originating switching center, to which the incoming call was delivered from the public switching center, to redirect the incoming call to a designated party. The originating mobile switching center executes program instructions to redirect the incoming call and to remove telephone facilities to the serving mobile switching center.
Numerous other advantages and features of the present invention will become readily apparent from the detailed description of the invention and the embodiments thereof, from the claims, and from the accompanying drawings.